Musannaf Ibn Abi Shayba 7:98

Abu Khalid al-Ahmar narrated to us, from Uthman ibn al-Aswad, who said: A man from my family died and bequeathed a slave (to be freed). I found a slave whose father had married his mother without the permission of his master. I asked Ata about it, and he said: "I dislike that."